The present invention relates to an improved easy-open container wall and method of making the same. More particularly, the invention relates to an easy-open container wall comprising a line of weakness in the container wall defining a tear portion at least partially removable from the container wall and a tab connected to the tear portion of the container wall and having a line of weakness severing nose end, a lifting end and hinge means for permitting hinged movement of one portion of the tab relative to another portion along a hinge line to bring the nose end into forceable engagement with the container wall to rupture the line of weakness and bend a segment of the tear portion inwardly upon lifting the lifting end of the tab.
In known commercially-used easy-open structures for containers of the aforementioned type the pull tab is generally secured to the sheet material container wall panel by a rivet head which is press-formed from the sheet material wall panel as in U.S. Pat. No. 3,366,270, for example. FIGS. 1-3 of the drawings illustrate such a known arrangement wherein a pull tab 1 is secured to a sheet material container wall panel 2 by a rivet head 3 which is press-formed from the sheet material wall panel. The rivet head extends through an opening in a hingedly mounted attaching panel 4 of the pull tab located intermediate the ends of the pull tab and extending away from the nose end thereof. The pull tab 1 functions as a lever during opening when the handle end 5 of the pull tab is lifted to pivot the majority of the pull tab relative to the attaching panel about a hinge line 6 to bring the nose end 7 of the pull tab into forceable engagement with the wall panel 2 to rupture a scoreline 8 therein and bend inwardly a segment of a tear portion 9 defined by the scoreline.
One problem associated with this prior art easy-open structure for containers is that when the pull on the pull tab is other than a longitudinal pull, there is a tendency for the pull tab to twist and to tear transversely across the hinge line. The pull tab is also subject to tearing out and structural failure adjacent the rivet head when the pull tab is being lifted upwardly and rearwardly as shown in FIG. 3 to tear the movable wall portion from the container wall panel. Further, this arrangement is problematical in that the pull tab is free to rotate about the rivet head so that it can become misaligned with respect to the scoreline in the container wall panel thereby additionally increasing the likelihood of structural failure of the pull tab at the hinge line or adjacent the rivet head during opening.
There have been numerous attempts in the prior art to avoid or minimize the aforementioned problems with the easy-open container wall of the type illustrated in FIGS. 1-3. For example, in U.S. Pat. No. 3,593,877 it is proposed to provide opposing semicircular slots in the pull tab for receiving a dimple which is formed in the removable panel portion so as to restrain the pull tab against rotation to maintain the nose of the pull tab aligned with the scoreline. However, this additional feature does not guard against twisting or misalignment of the tab which may occur as the handle end of the pull tab is being lifted nor does it aid in preventing tearing out and structural failure of the pull tab about the rivet head as the pull tab is being lifted upwardly and rearwardly during tearing of the removable panel portion from the container wall panel.
In U.S. Pat. No. 3,559,842 a pull tab with hinged attaching panel is disclosed wherein the end portions of a concavely shaped cut defining the attaching panel are reversely turned so as to terminate in a direction opposite from that of the normal tearing stress placed upon the body portion of the pull tab during opening thereby reducing the tendency of the pull tab to twist and tear transversely across the hinge line. However, tearing out and structural failure of the pull tab about the rivet head during opening remains a possibility with this structure.
An object of the present invention is to provide an easy-open container wall of the aforementioned type which avoids the above-discussed problems and disadvantages of the prior art. More particularly, an object of the present invention is to provide an easy-open container wall which is highly resistant to tearing out and structural failure during opening and which will not become misaligned with respect to the line of weakness in the container wall panel.
These and other objects of the present invention are attained by providing an easy-open container wall comprising a line of weakness in the container wall defining a tear portion at least partially removable from the container wall, a tab having a line of weakness severing nose end and a lifting end and having hinge means for permitting hinged movement of one portion of the tab relative to another portion of the tab along a hinge line to bring the nose end into forceable engagement with the container wall to rupture the line of weakness and bend a segment of the tear portion inwardly upon lifting the lifting end of the tab, and attachment means for attaching the tab to the tear portion at locations on both sides of the hinge line.
According to a disclosed, preferred embodiment of the invention the pull tab includes a hingedly mounted attaching panel located intermediate the ends of the pull tab and extending away from the nose end thereof. The attaching panel is an integral part of the tab and is defined by a concavely shaped cut opening towards the nose end of the tab. The pull tab is connected to the tear portion of the container wall by at least one weld connecting the attaching panel of the tab to the tear portion of the container wall panel on the side of the hinge line away from the nose end of the tab and by at least one weld connecting the tab to the tear portion of the container wall panel on the side of the hinge line toward the nose end of the tab. The disclosed preferred embodiment of the method of the invention involves welding the tab to the container wall on both sides of the hinge line by means of a high energy density welding process wherein the energy density is at least 10.sup.6 watts/inch.sup.2 such as with laser welding.
By attaching the tab to the tear portion of the container wall at locations on both sides of the hinge line of the pull tab, the alignment of the tab on the container wall is maintained so that the nose end of the tab remains positioned adjacent the line of weakness in the container wall and at the same time the invention offers the additional significant advantage that during opening the tendency of the tab material to be torn or pulled around its connection with the container wall is avoided since the highly stressed connections experience essentially shear stress during opening.
These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, one embodiment in accordance with the invention.